1. Field of the Invention
The present invention generally relates to laser scanning systems and, more particularly, to portable laser scanning arrangements for and methods of evaluating and validating bar code symbols such as Universal Product Code (UPC) symbols.
2. Description of the Prior Art
The grocery and food processing industries have recently developed a universal product code to uniquely designate each assigned product with a series of lines and spaces of varying widths, which pattern decodes to a multiple digit representation. Each such pattern is printed on the labels of even small items, and each line of the pattern therefore must be printed with a rather high degree of graphic precision. Typically, the supermarket check-out counter is provided with a built-in laser scanner and associated electronic circuitry operative for automatically decoding the pattern printed on the product for check-out and inventory purposes.
The graphic arts industry has had considerable difficulty in printing the labels and packaging stock on a mass-production basis due to the necessity of having to print the lines with the appropriate widths and against the appropriate background color. In view of the high production rates involved for grocery products such as soda, beer, milk carton stock, etc., poor quality control over the line widths and over the color contrast between the line color and the background color results in a loss of considerable stock.
Other than the above-described laser scanning systems built into the check-out counters of supermarkets, the prior art has proposed laser scanning heads movable relative to and electrically connected with a console. However, the known laser systems have not proven to be altogether satisfactory for a variety of reasons. First of all, the movable scanning head is not truly portable in the sense that the operation of the packaged laser tube may be affected adversely when the laser is directly hand-held and the user conversely exposed to the hot laser. Secondly, the known heads do not have the capability of increasing measurement accuracy by generating a two-axis scanning pattern comprising a plurality of equidistantly spaced apart parallel scanning lines over at least one-half of the height of the bar code symbol pattern, nor the capability of selecting between a single line scan or the above-described multiple line scan. Thirdly, the known systems do not provide a viewport of sufficient size or illumination to permit a user to properly and reliably superimpose the line scan across the pattern. Fourthly, the known systems do not provide for appropriate synchronization between both axes of scan. Fifthly, the known portable systems rely exclusively on expensive miniature rotary mirrored polygons, galvanometer movements or tuning forks to provide scanning. Sixthly, the bar width measurements taken by the movable scanning head are subject to a consideral amount of noise and modulation, thereby leading to inaccurate measurement evaluatic and possible decoding errors. Finally, other ease of operation and evaluation criteria requested by the graphic arts industry have not yet been embodied in a laser scanning system equipped with a portable scanning head.